The present invention relates to a switch arrangement or mechanism for supplying a load with current from an alternating current source, by means of phase shift control of the alternating voltage, the switch mechanism having anti-parallel thyristors connected in series with the load, and a monostable trigger stage controlling the thyristors. Such switch arrangements are used primarily for the low-loss reduction of the line voltage to the operating voltage of the load.
In one known switch mechanism of the above mentioned type, the monostable trigger stage is supplied with voltage via a capacitor which is connected in parallel in each case to a thyristor. The input of the monostable trigger stage is connected via a variable threshold resistor into the charging circuit of the capacitor. As a result of the variable threshold resistor the switching arrangement can be so adjusted that the load is fed its predetermined operating voltage regardless of the amount by which the line voltage exceeds the operating voltage of the load.
The disadvantage of this switch arrangement is that after connection of the switch mechanism to a line voltage having an effective value lying above the operating voltage of the load, the switch arrangement must first of all be adjusted by means of the variable resistor so that the operating voltage of the load is reached. Upon transfer to a current supply source of a different line voltage, a readjustment of the switch arrangement must be effected in order to feed the load with its proper operating voltage. Furthermore, this switch arrangement cannot produce a uniform load voltage when there are variations in the line voltage, as the load voltage will vary in the same ratio as the line voltage.
A first object of the invention, therefore, is to create a switch arrangement of the general type above mentioned, which makes it possible, without switching or special adjustment, to connect the load to various supply lines of different line voltages and yet supply the load with a constant operating voltage.
A second object of the invention is to provide switch mechanism of the general type above mentioned, so designed as to make it possible to use the switch mechanism with alternating current sources of different frequencies, while nevertheless providing an output of operating current of a constant or uniform voltage, notwithstanding variations in frequency or variations in voltage of the alternating current supply, and without requiring any special switching or adjustment on the part of the user of the switch mechanism.
It will be readily appreciated that switch mechanism accomplishing these objects will be very beneficial and desirable, for it will enable an appliance requiring a predetermined supply voltage to be used in various different countries or locations where the available alternating current supply has different voltages or different frequencies or both, so that the user may simply plug his switch mechanism and its connected appliance or load into an available alternating current supply socket or outlet, without having to determine first what voltage or what frequency is provided by the outlet, and without danger of damage to his appliance or load.